Continuously manufactured flexible conduit

ABSTRACT

A wire is fed from a supply roll to a device which twists the wire on its longitudinal axis and continuously forms the twisted wire into a non-rotating helical coil. The coil is fed directly from the device through a plastic tube extruding head by a rotatable screw which extends within the coil, and a vacuum is created within the tube as it is extruded over the coil to shrink the tube between the turns of the coil. The coil reinforced tube may then be fed through a device which covers the tube with a continuous fabric member, and the covered tube is then fed through another extruder head which extrudes a second tube over the fabric member and shrinks the second tube onto the fabric member and the first tube. The coil feeding screw, the fabric member forming device, the extruders, and the tube feeding devices are driven at speeds correlated with the speeds of twisting and feeding the wire to provide a continuous conduit forming operation.

United States Patent 1191 Kleykamp et al.-

[ CONTINUOUSLY MANUFACTURED FLEXIBLE CONDUIT [75] Inventors: Donald L.Kleykamp, West Carrolton, Ohio; Ivan Gaster; Vernon D. Browning, both ofWaynesville, NC; Homer N. Holder, Sylva, NC.

[73] Assignee: Dayco Corporation, Dayton, Ohio [22] Filed: Feb. 13, 1973[21] Appl. No.: 331,756

Related U.S. Application Data [63] Continuation ofSer. No. 89,333. Dec.13. 1970. Pat.

[52] U.S. Cl. 156/425 [51] Int. Cl B3lc [58] Field of Search 29/527.4,202.5; 156/86,

[56] References Cited UNITED STATES PATENTS 3,526,692 9/1970 Onaka425/109 X 1451 Apr. 9, 1974 Primary E.\'aminerCharles W. LanhamAssistant E.\uminerRobert M. Rogers [57] ABSTRACT forced tube may thenbe fed through a device which covers the tube with a continuous fabricmember, and the covered tube is then fed through another extruder headwhich extrudes a second tube over the fabric member and shrinks thesecond tube onto the fabric member and the first tube. The coil feedingscrew, the fabric member forming device, the extruders, and the tubefeeding devices are driven at speeds correlated with the speeds oftwisting and feeding the wire to provide a continuous conduit formingoperation.

8 Claims, 7 Drawing Figures PATENTEDAPR 9 1914 SHEET 1 (IF 2@MJJOmE-ZQP. I l 1 1 1H CONTINUOUSLY MANUFACTURED FLEXIBLE CONDUIT gThis is a continuation of U.S. Pat. application Ser. No. 89,333, filedNov. 13, 1970 now U.S. Pat. No.

BACKGROUND OF THE INVENTION The present invention relates to acontinuously manufactured flexible conduit which is used for conveyingfluids such as air, and the method and apparatus for manufacturing thisconduit. More specifically, the conduit hereinafter described is thetype having a helical reinforcing coil formed of axially spaced turns,about which is placed a plastic flexible tube. The purpose of this typeof conduit is to provide passage ofthe fluid which it is conveyingwithout substantial leakage, while at the same time being sufficientlystrong to prevent collapse, light in weight for portability, and yetsufficiently flexible to permit bending. I

.Conventionally the helical coil is made of a plastic coated wire whisis formed with axially spaced turns and the tube is bonded to the turnsof the wire to form a unitary product. Occasionally such a conduit ismade with a fabric reinforcement such as a braided or knitted member,which is placed over the tube; optionally, a further plastic tube isplaced over this fabric member. One such conduit is disclosed in U.S.Pat. No. 3,279,502, of common assignment, in which a series of coils isshown as being successivley fed through a plastic extruder which thencovers the coils with a tube. The fabric member is placed over this tubewhich is then passed through another process which adds an outer member.In this patent the coils are stated as being capable of joining end toend in order to form a continuous conduit. This might be done, forexample, by a welding operation as shown in U.S. Pat. No. 2,963,749.Such an operation, however, requires a complex mechanism and does notlend itself fully to a continuous process.

It has also been proposed to produce a reinforced conduit by wrapping areinforcing wire on a rotating mandrel and feeding it through'a plasticextruding head. U.S. Pat. No. 3,526,692 disclosessuch a device, but thisrequires that the plastic pipe be rotatedas it extruded, and it wouldthus not be suitable for continuously producing flexible reinforcedcorrugated conduit which must be coiled into a roll after cooling.

SUMMARY or THE INVENTION The present invention is directed to animproved method and apparatus for continuously producing a flexiblereinforced-corrugated conduit which involves the feeding of'a wire(which may have a plastic coat ing) from a supply roll, continuouslyforming the wire into a non-rotating helical coil, and continuouslyfeeding the coil through a plastic extruder head which ex-.

trudes a plastic tube onto the coil and shrinks the tube onto the ,coilto form helical co'nvolutions between the turns. The invention alsoprovides for continuously its longitudinal axis and then rolls or formsthe twisted wire into a helical coil. The speed of twisting of the wireis correlated with the speed of feeding the wire so that the devicecontinuously generates or produces a non.-

rotating helical coil of predetermined diameter. The coil is fed fromthe forming device onto a feed screw which extends through a plasticextruder head and is driven at a speed correlated to the speed at whichthe helical coil is produced.

A plastic tube is extruded onto the helical coil at the discharge end ofthe extruder head, and a vacuum is produced within the coil to shrinkthe extruded tube radially inwardly between the wire turns of thecoil'and to form a positive bond between the plastic tube and theplastic coating on the wire. The conduit may be cut into predeterminedlengths or coiled into a roll, or the conduit may be fed directlythrough a braiding or knitting machine to form a fabric covering memberon the reinforced plastic tube. I

The fabric covered tube is fed through a second plastic extruder headwhich covers the fabric member with an outer plastic tube and shrinksthe tube onto the fabric member and the first tube by introducing avacuum between the first tube and the second tube as the latter is beingextruded. The wire twisting and feeding means, the spring feeding screw,each of the extruders, the fabric covering machine and the two tubefeeding conveyors are all driven at correlated speeds according to thedesired production rate of the reinforced flexible conduit.

Additional features and advantages of the invention will be apparentfrom the following description,.the accompanying drawings, and theappeneded claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a general diagrammatic planview of apparatus forv continuously producing a reinforced flexibleconduit in accordance with the invention.

FIG. 2 is a diagrammatic plan view of apparatus for receivingthe-conduit produced by the apparatus shown in FIG. 1 and continuouslyproducing a double plastic wall flexible corrugated conduit.

FIG. 3 is a fragmentary section taken generally on' line 3 -3 of FIG. 1.FIG. 4 is a fragmentary section taken generally on the line 4-4 of FIG.3.

FIG. 5 is an axial section .of an extruder head included in theapparatus shown in FIG. 1.

FIG. 6 is an enlarged fragmentary section of the discharge end of theextruder headin FIG. 5 and showing the forming of a single plastic wallconduit.

FIG. 7 is a fragmentary section similar to FIG. 6 of the extruder headincluded in the apparatus in FIG. 2 and showing the forming of a doubleplastic wallconduit.

I DESCRIPTION OF THE PREFERRED EMBODIMENT rollers (FIGS. 1 and 3) form anip which receives the wire W before the wire enters the spring formingdevice 15 and serve to prevent twisting of the wire between the supplyroll 16 and the roller 18. The forming device 15 includes a rotatablebase member 20 having a tubular inlet portion 21 supported by ananti-friction bearing 22, and 'an aligned tubular outlet portion 23supported by an anti-friction bearing 24. The base member 20 thusrotates on the axis of the tubular portion 21 and 23 and is driven by avariable speed motor 25 through abelt 26 directed around a pulley 27secured to the tu- *bular inlet portion 21 of the base number.

The plastic coated wire W is directed from the antitwist rollers 18through a curved guide tube 28 located withinthe tubular inlet portion21 of the base member '20, and is then directed around a feed wheel 30having a peripheral recess 31 which. receives the wire. The

wheel 30 is mounted on. oneend portion of a shaft 33 which is rotatablysupported by an anti-friction bearing 34 retained within a hub portion36 of the base member 20. A beveled gear 38 is secured to the oppositeend portion of the shaft 33 and meshes with another bevel 1 gear 39rotatably supported by an anti-friction bearing 41 mounted on the inletportion 21 of the base member 20. A pulley 42 is rigidly connected tothe gear 39 and is driven by a variable speed motor 45 through a V-beltA plurality of rollers 48 are arranged around the periphery of the feedwheel 30 and are rotatably supported on the base member 20. The rollers48 have resilient outer surfaces and serves to retain the wire W withinthe recess 39 on the outer surface of the feed wheel 30. Thus when thewheel 30 is rotated by the motor 45, the wire W is pulled or fed fromthe supply roll 16, between 'he rollers 18, and through the curvedguide'tube 28.

The wire W-iswrapped one turn around the feed wheel 30 and-is directedfrom the wheel 30 between a setof external wire forming rollers 52 (FIG.4) and an and 53 are set so that after the wire W is coiled and springsback slightly, the outer diameter of the coil S is slightly less thanthe'inner diameter of the tubular outlet portion 23 of the basemember'20. 7

As shown in FIG. 1, the variable speed motors 25 and 45 are operatedfrom a main controller '55. As the wire W is being fed through theforming device by rotation of the wheel 30, the base member is rotatedby I the motor to cause twisting of the wire W on its lon- 'gitudinalaxis between the feed wheel and the rollers 18. The motors 25 and 45are/adjusted or correlated so i that during'each revolution of the basemember 20, sufficient wire W is fed by the wheel 30 to form oneconvolution or-turn of the helical coil S; As a result, the

coil is continuously formed and feeds through the out-.

let portion 23 without any rotation of the coil on its longitudinalaxis.

ing from the scope of the invention. PrferablyQhowever, the nonrotatinghelical coil is produced by twisting of a wire on its axis at aspeedcorrelated with the longitudinal or axial feed of the wire.

Referring to FIG. 1 and 5, the helical coil S'is fed from the formingdevice 15 directly into an extrudcr head 60 which receives a flowableplastic material such asa syntheticor natural rubber or a thermoplasticmaterial, from an extruder barrel 62 enclosing a screw 63 driven by avariable speed motor 64. The extruder head 60 includes a hollowcylindrical housing 65 (FIG. 5) which is secured to the barrel 62 by acoupling flange 66 defining an inlet 67 which extends through thehousing 65. The housing 65 has a cylindrical bore 69 which whichcooperates with a rearward portion 77 to define an annular tapereddistributing chamber 78 extending from the inlet 67. The rearwardportion 77 of the unit defines an elongated cylindrical bore 80 whichextends through a tubular sleeve portion 81 projecting axially throughthe distributing chamber 78. An annular extrusion die 85 is positionedbetween the housing flange 71 and the forward portion 76 of the unit 75and has a cylindrical bore oropening 86 which receives and cooperateswith the sleeve portion 81 to define an annular cylindrical dischargeorifice 88. The die 85 ispositioned radially relative to the sleeveportion 81 by a set of four uniformly spaced screws 89. I

An elongated feed screw 90 extends through the bore 80 within the unit75 and has a single external helical groove 92 with a depthapproximately the same as the diameter of the wire W. The pitch of thegroove 92 corresponds with the spacing between the convolutions or turnsof the coil S, and the screw 90 receives the coil directly from theforming device 15. The screw 90 is rotatably supported withinthe unit7.5,by an antitapered roller bearing 96. The bearings are retainedwithin corresponding counterbores 97- and .98 by a threaded annularfitting 99. The inner races'of the bearings 94 and 96 are press fittedon the screw 90, and the outer race of the tapered roller bearing 96 ispressed'axially by the fitting 99 so. that the screw 90 will rotatewithin the bore 80 without any lateral play or wobble. i i

The assembly of the body 75;and the screw 90 are retained within thehousing by an annular plate 101 and a series of screws 102. A sheaveorpullye 103 is press fitted on the leading projecting end portion of thescrew 90 andis driven by a belt 104 (FIG. 1) extending from a variablespeed motor 105. The motor 105 is also operated from the controller 55and -is controlled so that the screw 9 0 is rotated or driven at a speedcorrelated with the speed'ot the motors 25 and 45.

A radially extending passage. 108 is formed within the housing 64 andinsert unit 75 of the extruder head 60 and is connected by a line 109 toa suitable vacuum source (not shown). The passage 108 extends inwardlyto the bore 80 adjacent a series of four radially extending ports 110(FIG. 5) formed within the screw 90. A passage 112 extends axiallythrough the screw 90 from the ports 110 to the discharge end of a screw90 and cooperates with the ports 110 to create a vacuum adjacent thedischarge end of the screw 90.

As the helical coil S is fed through the extruder head 60 by therotating screw 90, a plastic tube T is extruded from the orifice 88 inoverlying surrounding relation to the coil S. The hot plastic tube T isreduced or shrunk inwardly by the vacuum created through the passage 112and through the clearance space between the outer surface of the screw90 and the inner surface of the tubular sleeve portion 81 of the insertbody 75. The vacuum shrinking of the tube T produces a positive bondbetween the tube and the plastic coated wire W and also produces helicalconvolutions in the tube T between the turns of the wire W as shown inFIG. 6. The motor 64 for driving the feed screw 63 of the plasticextruder, is controlled according to the axial feed rate of the helicalcoil S so that the plastic tube T is extruded at a rate sufficient toprovide for the convolutions within the tube between the turns of thecoil S.

The extruded plastic tube T and the reinforcing helical coil S form anon-rotating tubular conduit C which is directed through a coolingdevice 115 (FIG. I) where the conduit passes through either a waterfilled trough or water sprays directed from a series of nozzles 117.After the extruded tube T is cooled, the conduit C may be dried by ablast of hot air from a plurality of nozzles 1 l8 and then wound onto aroll, or cut into sections of predetermined length.

MODIFICATION A further embodiment of the invention is illustrated inFIGS. 2 and 7, in which conduit C, after cooling and drying as above,may be fed directly into a braiding or knitting machine 125 which formsa tubular fabric member K tightly overlying or surrounding the plastictube T. The member K may be formed by a knitting head, for example, asdisclosed in U.S. Pat. No. 2,259,384, or may be formed by a braidingmachine, for example, as disclosed in U.S. Pat. No. 3,038,523. Thebraiding or knitting machine 125 is driven by a variable speed motor 128which is also operated from the main controller 55. The resultingassembly is fed through the machine 125 by a pair of opposingcaterpillar-type conveyors 130 which are also driven by a variable speedmotor 132 operated from the controller 55. The spacing between theconveyors 130 is precisely adjusted so that the conduit is positivelygripped without significantly compressing the conduit.

The conveyors 130 also feed the conduit assembly from the machine 125directly into another extruder head 60 which is constructedsubstantially identical to the extruder head 60 except that the feedscrew 90 and its corresponding drive is omitted. Accordingly, the

components of the extruder head 60 carry the same reference numbers asthe corresponding components of the extruder head 60. As shown in FIG.7, the extruder 60' produces an outer plastic tube T which overlies orsurrounds the conduit assembly and is in direct contact with fabricmember K. The plastic tube T is shrunk onto the assembly by the partialvacuum which is created at the discharge end of the extruder fed fromthe extruder head 60 through another water cooling device 115 by anotherset of caterpillar-type conveyors 130 driven by a corresponding variablespeed motor 132 operated from controller 55. In a manner as mentionedabove in connection with the single plastic tubular wall conduit C, thenon-rotating double plastic-wall conduit C may be coiled into -a,roll orcut into lengths.

From the drawings and the above description, it is apparent that theapparatus and method of the invention provide several desirable featuresand advantages. For example, the device 15 is effective to twistandfeed' the plastic coated wire W at relative correlated speeds forcontinuously producing a non-rotating helical coil S. Furthermore, thespeed of the motor 105 is controlled in accordance with the speeds ofthe motors 25 and 45 to feed the continuously produced non-rotating coildirectly through the extruder head 60 for continuously producing theflexible reinforced tubular conduit C.

Another important feature is provided by introducing a vacuum within theextruder head 60 and the feed screw 90 through the line 109 to causeshrinking of the plastic tube T onto the coil S and between the 'wireconvolutions immediately after the tube is extruded from the head 60 andwhile the tube is still hot and pliable. The screws 89 also provide theadvantage of adjusting the die 85 radially to provide preciseconcentricity between the die bore 86 and the tubular sleeve portion 81of the insert member 75. This not only provides for obtaining plastictubesof precisely uniform wall thickness, but also provides forinterchanging dies 85 when it is desired to change the wall thickness ofthe tube T.

As disclosed in connection with FIGS. 2 and 7, the present inventionfurther provides for continuously producing a reinforced conduit Chaving a multiple layer wall consisting of the inner-plastic tube T, atightly wound fabric member K and the outer plastic tube T Byintroducing a vacuum into the second extruder head 60 through the line109, the outerplastic" convolutions within the" outer plastic tube Tbetween within the outer tube T through the clearance'space between theinner cylindrical surface of the tubular the turns of the coil S and toform a permanent bond between the plastic tubes and the fabric member.

It is also within the scope of the invention to modify the formingdevice 15 and the feed screw 90 of the extruder head 60 for continuouslyproducing a flexible reinforced conduit wherein the reinforcing coil isconstructed of two or more insulated electrical wires. Such a conduit iscommonly used with a canister type vacuum sweeper for transmittingelectrical power from the main unit to a portable suctionheadincorporating a motor driven beater. That is, the forming device 15 maybe easily modified to receive two or three coated or insulated wires Wto form the wires into a double or triple helical coil. A modified feedscrew 90 having corresponding double or triple helical grooves wouldthen be used for feeding themultiple turns through the extruder head 60.It should also be understood that a flexible reinforced conduitconstructed in accordance with the invention, may be provided withlongitudinally extending reinforcing wires or cords such as disclosed inU.S. Pat. No. 3,058,493. These wires would be fed directly into theextruder head 60 or 60 and be located between the coil S and the plastictube T or between the tube T and the fabric member K.

j While the method therein described, and the form of apparatus forcarrying this method into effect, constitute preferred embodiments ofthe invention, it is to be understood that the invention is not limitedto this precise method and form of apparatus, and that changes may bemade in either without departing from the scope of the invention whichis defined in the appended claims. I

' 1; Improved apparatus for producing a continuous flexible reinforcedtubular conduit having a uniform structure along the length thereof,said apparatus comprising means for supporting a relatively large supplyroll of wire for rotation on a stationary axis, a rotary coil-formingunit separate from said roll-supporting means and including means fordeforming the wire beyond its elastic limit into a helical coil, meansfor supporting said coil-forming unit for rotation, means for directingthe wire from said roll-supporting means to said wire deforming means,means for driving said rotary coil-forming unit to produce a continuousnonrotating helical coil having continuous convolutions of uniformdiameter, an extruder head having means for receiving a plastic materialin a flowable condition, means for feeding said coil axially in anonrotating manner from said coil-forming unit through said extruderhead, means for correlating the speed of said coil-feeding means withthe speed of said means for driving said coil-forming unit to effect asmooth continuous uniform flow of the helical coil from said coilformingunit through said extruder head, means within said extruder head forforming a tube of a plastic mate rial around said coil, and means forshrinking said plastic tube onto said coil.

2. Apparatus as defined in claim 1 wherein-the axis of the wireroll-supporting means is disposed at substantially a right angle withthe axis of rotation of said rotary coil-forming unit.

' means defining a generally cylindrical bore for receiving the helicalcoil as it is being formed.

4. Apparatus as defined in claim 1 wherein said extruder head includesmeans defining a generally cylindrical bore for receiving the helicalcoil, and the axis of said bore is substantially aligned with the axisof rotation of said coil-forming unit.

5. Apparatus as defined in claim 1 wherein said means for directing thewire includes a wheel on said rotary coil-forming unit, and said wheelhas an axis of rotation disposed at a substantially right anglerelativeto the axis of rotation of said coil-forming unit,

6. Apparatus as defined in claim 1 wherein said rotary coil-forming unitincludes means for gripping the wire and pulling it from the wire supplyroll supported by said roll-supporting means.

7. Apparatus as defined in claim 1 wherein said means for supporting thewire roll and said extruder head are disposed generally axially onopposite ends of said rotary coil-forming unit.

8. lmproved apparatus for producing a continuous flexible reinforcedtubular conduit having a uniform structure along the length thereof,said apparatus comprising means for supporting a relatively large supplyroll of wire for rotation on a stationary axis, a rotary coil-formingunit separate from said roll-supporting means and including means fordeforming the wire beyond its elastic limit into a helical coil, meansfor supporting said coil-forming unit for rotation, means for directingthe wire from said roll-supporting means to said wire deforming means,means for driving said rotary coil-forming unit to'produce a continuousnonrotating helical coil having continuous convolutions of uniformdiameter, said supporting means for said ro tary coil-forming unitincluding means defining a generally cylindrical bore for receiving thehelical coil as it is being formed, an extruder head having means forreceiving a plastic material in a flowable condition, means for feedingsaid coil axially in a nonrotating manner from said coil forming unitthrough'said extruder head, means for correlating the speed of saidcoil-feeding means with the speed of said means for driving saidcoil-forming unit to effect a smooth contin uous uniform flow of thehelical coil from said coilforming unit through said extruder head,means within said extruder head for forming a tube of a plastic materialaround said coil, means for shrinking said plastic tube onto said coil,said means for supporting the wire roll and said extruder head beingdisposed generally axially on opposite ends of said rotary coil-formingunit.

* IF =l= l UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent3,802,991 Dated April 9, 1974 Inventor(s) DONALD L. KLEYKAMP, ET. AL.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

On the cover sheet insert The portion of the term of this patentsubsequent to April 3, 1990, has been disclaimed.

Signed and sealed this 21st day of Jenuary 1975.

(SEAL) Attest:

MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents USCOMM-DC 60376-P69 15. GOVERNMENT PRINTING OFFICE: a 69- 93 0FORM PO-IOSO (10-69)

1. Improved apparatus for producing a continuous flexible reinforcedtubular conduit having a uniform structure along the length thereof,said apparatus comprising means for supporting a relatively large supplyroll of wire for rotation on a stationary axis, a rotary coil-formingunit separate from said rollsupporting means and including means fordeforming the wire beyond its elastic limit into a helical coil, meansfor supporting said coil-forming unit for rotation, means for directingthe wire from said roll-supporting means to said wire deforming means,means for driving said rotary coil-forming unit to produce a continuousnonrotating helical coil having continuous convolutions of uniformdiameter, an extruder head having means for receiving a plastic materialin a flowable condition, means for feeding said coil axially in anonrotating manner from said coil-forming unit through said extruderhead, means for correlating the speed of said coil-feeding means withthe speed of said means for driving said coil-forming unit to effect asmootH continuous uniform flow of the helical coil from saidcoil-forming unit through said extruder head, means within said extruderhead for forming a tube of a plastic material around said coil, andmeans for shrinking said plastic tube onto said coil.
 2. Apparatus asdefined in claim 1 wherein the axis of the wire roll-supporting means isdisposed at substantially a right angle with the axis of rotation ofsaid rotary coil-forming unit.
 3. Apparatus as defined in claim 1wherein said supporting means for said rotary coil-forming unit includesmeans defining a generally cylindrical bore for receiving the helicalcoil as it is being formed.
 4. Apparatus as defined in claim 1 whereinsaid extruder head includes means defining a generally cylindrical borefor receiving the helical coil, and the axis of said bore issubstantially aligned with the axis of rotation of said coil-formingunit.
 5. Apparatus as defined in claim 1 wherein said means fordirecting the wire includes a wheel on said rotary coil-forming unit,and said wheel has an axis of rotation disposed at a substantially rightangle relative to the axis of rotation of said coil-forming unit. 6.Apparatus as defined in claim 1 wherein said rotary coil-forming unitincludes means for gripping the wire and pulling it from the wire supplyroll supported by said roll-supporting means.
 7. Apparatus as defined inclaim 1 wherein said means for supporting the wire roll and saidextruder head are disposed generally axially on opposite ends of saidrotary coil-forming unit.
 8. Improved apparatus for producing acontinuous flexible reinforced tubular conduit having a uniformstructure along the length thereof, said apparatus comprising means forsupporting a relatively large supply roll of wire for rotation on astationary axis, a rotary coil-forming unit separate from saidroll-supporting means and including means for deforming the wire beyondits elastic limit into a helical coil, means for supporting saidcoil-forming unit for rotation, means for directing the wire from saidroll-supporting means to said wire deforming means, means for drivingsaid rotary coil-forming unit to produce a continuous nonrotatinghelical coil having continuous convolutions of uniform diameter, saidsupporting means for said rotary coil-forming unit including meansdefining a generally cylindrical bore for receiving the helical coil asit is being formed, an extruder head having means for receiving aplastic material in a flowable condition, means for feeding said coilaxially in a nonrotating manner from said coil-forming unit through saidextruder head, means for correlating the speed of said coil-feedingmeans with the speed of said means for driving said coil-forming unit toeffect a smooth continuous uniform flow of the helical coil from saidcoil-forming unit through said extruder head, means within said extruderhead for forming a tube of a plastic material around said coil, meansfor shrinking said plastic tube onto said coil, said means forsupporting the wire roll and said extruder head being disposed generallyaxially on opposite ends of said rotary coil-forming unit.